Almost all present electronic systems require pushbutton switches that furnish signals to digital logic for system control. However, all pushbutton switches with dry mechanical contacts exhibit a "bounce" characteristic i.e., intermittently opening and closing for a short period after activation. When coupled directly with digital logic, this results in multiple or false detection of switch operation. Therefore, all such signals must be buffered, and the circuits used are termed "debounce" buffers or circuits. Two schemes for contact debounce are in common use. One is an active circuit which has been used featuring cross coupled nand gates. The primary disadvantage of this circuit is that it requires two wires from the pushbutton to the debounce circuit. This can lead to a large interface problem with complex control panels.
The second prior art apparatus is a passive circuit which uses an RC time constant to eliminate contact bounce. There are three disadvantages to this circuit. The first disadvantage is the slow rising edge. The second disadvantage is the analog discrete components. The third disadvantage is that different switches exhibit different bounce characteristics so no R/C combination is the optimum for all circuits. The present invention offers advantages over the prior art. It is an active circuit but with only one wire interfacing the pushbutton and the debounce circuit and includes fewer parts such as one resistor for a significant parts saving.